1. Field of the Invention
The present invention relates to wireless communication systems, but more particularly, to a method and system for attaining sectorization in a cellular communication system utilizing a single broadband processing unit.
2. Discussion of the Prior Art
In order to provide multi-channel voice and data communications over a broad geographical area, wireless communication providers currently install base station transceivers in protected and maintainable structures, known as cell sites. A cell site encompasses an antenna, a tower or building upon which the antenna is mounted, high-power amplifiers, duplexers, transmitters, receivers and broadband processing equipment. The broadband processing equipment channelizes and combines digital signals on multiple channels that are associated with respective subscribers. The digital signals, however, are communicated over the air with subscribers in the analog domain. Thus, the base station equipment further includes analog-to-digital and digital-to-analog converters, depending on the direction of information flow, as described in commonly owned U.S. Pat. Nos. 5,535,240 and 5,592,480 which issued Jul. 9, 1996 and Jan. 7, 1997, respectively, to Ronald R. Carney, et al., incorporated herein by reference.
The cell itself is an area on the ground that is generally depicted as a hexagon. This is the simplest way to illustrate the cellular idea, but in reality, the actual shape of the cell and the coverage provided by the radiated signal from the cell site is rarely as regular, uniform and clearly defined. The actual shape of the cell depends upon the contours and the condition of the terrain surrounding the cell site. Factors such as the size and number of trees and/or the degree of urbanization determine how large an area one cell can cover. The cell may itself be sectorized wherein it is provided with an antenna designed to concentrate energy in an arc of 120 degrees rather than the usual 360 degrees. Different frequencies may be used for each sector, and these frequencies may be repeated among cells. Using the sectorization, the cell site is able to accommodate communication for a greater number of subscribers. The instant application is directed to sectorization which is sometimes referred to as cell-splitting.
Each sector is configured to provide two-way (duplex) multi-channel communication capability for only a limited portion of the frequency spectrum that is allotted to the wireless communication service provider. A typical cellular communication channel consists of a pair of frequencies, one for each direction of transmission, used for full-duplex operation. A typical transceiver consists of multiple sets of discrete receiver and transmitter signal processing components in order to service a particular portion of the frequency spectrum, usually 400 30 Khz channels within a 12 MHZ bandwidth. The receiver section of a typical transceiver includes a dedicated set of signal processing components, including a front end, an intermediate frequency (IF) section and a baseband section.
A primary limitation in current cellular communication systems is that a service provider is only allocated a fixed number of frequencies with which to handle subscriber calls. Typically, there must be a 35 mile separation between cells using the same frequency set, so that subscribers communicating on the same frequencies do not interfere with one another. Frequency reuse allows subscribers to use the same frequencies in adjoining cells without interference, thereby allowing a service provider to accommodate more subscribers.
Whenever a base station employs sectorization, however, each sector requires its own broadband processing unit to perform digital combining and channelizing. Unfortunately, such replication of digital processing equipment increases the complexity and expense of the base station.